A Risk-based Groundwater Modelling

Study for Predicting Thermal Plume

Migration from SAGD Well-pads

Rudy Maji, Ph.D., Golder Associates

Solaleh Khezri, M.Sc., AB Scientific Intern (Golder Associates)

Don Haley, M.Sc., Golder Associates

Michael De Luca, M.Sc., P.Geol., Brion Energy

Outline

Motivation

Problem Statement

Numerical Model Construction

Numerical Model Results

Summary and Conclusions

April 30, 2015 2

Motivation –

Why Thermal Plume Migration Matters

Elevated temperatures increase the mobilization of chemical

constituents that are naturally present in sediments.

Since the start of thermal in-situ oil sand production, increased levels of

Arsenic was observed in groundwater downgradient of several steam

injection wells at the Cold Lake site.

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Problem Statement –

Steam Assisted Gravity Drainage (SAGD)

April 30, 2015 4

Area of Interest

Problem Statement –

Conceptual Model of Heat Plumes Near Wellbores

April 30, 2015 5

Groundwater Flow

Aquitard

Aquifer

Aquifer

Aquitard

Aquitard

Problem Statement –

Modelling as a Screening Tool

Generic modeling can be used as a screening tool as one input into a

risk based assessment of solute migration from multiple SAGD well

pads.

If the risk at a particular well pad is considered potentially significant, site

specific models (deterministic or stochastic) can be developed to help

evaluate and quantify the risk of thermally enhanced solute migration.

Site specific model could also be used to aid in the design of the

Groundwater Monitoring Plan (GWMP), as directed in the DRAFT

Guidance for Groundwater Management Plans for In Situ Operations:

Assessing Thermally-Mobilized Constituents

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Numerical Modelling – SAGD Well-Pads in MacKay

River Commercial Project Area

April 30, 2015 7

Well-Pad AJ

Well-Pad AB

Well-Pad AA

Streams (SW Receptors)

Numerical Modelling –

Borehole Lithology Around Well-Pad AJ

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Model

LayerFormation

Horizontal

Hydraulic

Conductivity

(m/s)

Thickness

(m)

Layer 1 Undifferentiated overburden (Clay Silt Till) 1E-7 10

Layer 2 Undifferentiated overburden (Clay Silt Till) 1E-7 10

Layer 3 Undifferentiated overburden (Sand Till) 5E-5 5

Layer 4 Undifferentiated overburden (Clay Silt Till) 1E-7 10

Layer 5 Joli Fou Formation (Shale) 5E-8 10

Layer 6 Grand Rapids 4 Formation (Sandstone) 3E-4* 10

Layer 7 Grand Rapids Formation (Shale) 5E-8 5

Layer 8 Grand Rapids 5 Formation (Sandstone) 1.6E-5* 5

Layer 9 Grand Rapids Formation (Shale) 5E-8 5

Layer

10Grand Rapids 5 Formation (Sandstone) 1.6E-5* 10

Layer

11Grand Rapids 5 Formation (Sandstone) 1.6E-5* 10

* Hydraulic conductivity values derived from pumping tests.

Numerical Modelling –

Sources and Receptors

Sources Receptors

Pad AJ, Pad AA and Pad AB Surface water streams, Aquifers

(Overburden Aquifer, Grand Rapids 4

and 5)

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Numerical Model Construction –

Model Domain

April 30, 2015 10

Wells with Geology Logs

SAGD Steam Injection Wells

Model Domain

Well-Pad AJ

Well-Pad AB

Well-Pad AA

Numerical Model Construction –

Numerical Mesh

April 30, 2015 11

Well-Pad AJ

Well-Pad AB

Well-Pad AA

Element Size Around SAGD

Wells: <1 m to 9 m

April 30, 2015 12

Streams

• 11 Numerical Layers

• Each Layer 5 m to 10 m thick

• 9 Different Hydrostratigraphic Units

Numerical Model Construction –

3-Dimensional Numerical Block Model

Numerical Model Construction –

Boundary Conditions

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Average Hydraulic

Gradient: 0.25%

Constant Temperature of 5 ˚C

at Surface and Inflow Nodes

X

Y

Numerical Model Construction –

Heat Loss in the Steam Injection Well Versus Depth

April 30, 2015 14

Steam Temp= 230 ˚C

at surface

Steam Temp= 220˚C

at top of McMurray

Steam Temp= 226˚C

at bottom of Grand

Rapids 5

Numerical Model Construction –

Representative Steam Injector Design

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Numerical Model Construction –

Representation of a SAGD Well Using the BHE Boundary

April 30, 2015 16

Borehole Heat Exchanger

InjectionRecovery

InjectionRecovery

Numerical Model Results –

Calibration to Temperature Change Along the Wellbore

April 30, 2015 17

Recovery Injection

Numerical Model Results –

Modelling Cases

Case 1: Steaming of well-pad AJ for 38 years

Case 2: Steaming of all three well-pads for 38 years simultaneously and

movement of thermal plume after cession of steaming

April 30, 2015 18

Numerical Model Results – Case 1 (Single Well Pad):

Thermal Plumes at Well-Pad AJ

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Quaternary Aquifer

Depth: 20 m

Max Temp: 145.7 ˚C

KH= 5E-5 m/s

Grand Rapids 4

Depth: 45 m

Max Temp: 104 ˚C

KH = 3E-4 m/s

Grand Rapids 5

Depth: 80 m

Max Temp: 153 ˚C

KH = 1.6E-5 m/s

363

m

380

m

418

m

Note: After 38 years of steaming

Numerical Model Results – Case 2 (Cumulative Effects):

Thermal Plumes in Quaternary Aquifer - All 3 Well-Pads

April 30, 2015 20

363 m

367 m

366 m

KH = 5E-5 m/s

Depth: 20 m

Note: After 38 years of steaming

Numerical Model Results – Case 2 (Cumulative Effects):

Thermal Plumes in Grand Rapids 4 Aquifer

April 30, 2015 21

418 m

420 m

422 m

KH = 3E-4 m/s

Depth: 45 m

Note: After 38 years of steaming

Numerical Model Results – Case 2 (Cumulative Effects):

Thermal Plumes in Grand Rapids 5 Aquifer

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380 m

382 m

386 m

KH = 1.6E-5 m/s

Depth: 80 m

Note: After 38 years of steaming

Numerical Model Results – Case 2 (Cumulative Effects):

Vertical Profiles Through Each Well Pad

April 30, 2015 23

K=1E-7 m/sK=5E-5 m/sK=1E-7 m/sK=5E-8 m/sK=3E-4 m/s

K=1.6E-5 m/s

K=5E-8 m/s

Well Pad AJ

Well Pad AB

Well Pad AA

A

A

A

A’

A’

A’

K=1E-7 m/sK=5E-5 m/sK=1E-7 m/sK=5E-8 m/sK=3E-4 m/s

K=1.6E-5 m/sK=5E-8 m/s

Well Pad AJ

A A’

Well Pad AB

B B’

Well Pad AA

C C’380 mNote: After 38 years of steaming

A’

A

Numerical Model Results – Case 2 (Cumulative Effects):

Length of 50 ˚C Isotherm From Steam Injector

Depth (m) Length of 50 ˚C

Isotherm (m)

Hydraulic

Conductivity (m/s)

1 1.3 1E-7

10 4.6 m 1E-7

20 8.3 5E-5

25 8.6 1E-7

35 6.9 5E-8

45 5.2 3E-4

55 5.9 5E-8

60 7.5 1.6E-5

65 9.9 5E-8

70 13.4 1.6E-5

80 20 1.6E-5

90 22 1.6 E-5

April 30, 2015 24

Highest Aquifer K

Intermediate Aquifer K

Lowest Aquifer K

Note: After 38 years of steaming

Numerical Model Results – Case 2 (Cumulative Effects):

Temperature Increase in Underlying Aquifers

April 30, 2015 25

Well-Pad AB

Well-Pad AA

Well-Pad AA

Well-Pad AB

Grand Rapids 4

Grand Rapids 5

Quaternary

Grand Rapids 4

Grand Rapids 5

Quaternary

Note: Location is immediately downstream of the injector and below the streams

210 m

605 m

Numerical Model Results – Case 2 (Cumulative Effects):

Thermal Plume Migration after Cessation of Steaming

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Time= 0

Max T= 152.5 ˚C

Time= 50 years

Max T= 13.7 ˚C

Time= 10 years

Max T= 34.5 ˚C

Time= 25 years

Max T= 22 ˚C

380 m 520 m450 m

600 m

Time= 100 years

Max T= 10 ˚C

NOTE: Results are for Well Pad AJ

Summary and Conclusions

The distance from Pad AJ to the nearby stream is larger compared to that of

Pads AA and AB; hence, the simulated thermal plume from Pad AJ doesn’t

reach to the nearby streams.

The simulation results suggest that thermal plumes originating from the Pads AA

and AB would intersect the nearby streams, hence pose a greater risk compared

to the Pad AJ if solute migration is thermally enhanced.

The 50 0C temperature plume travels only a few tens of metres; hence, the

potential zone of Arsenic mobilization is simulated to be within a few tens of

metres, provided the enhanced mobilization effect decreases as temperature

drops.

April 30, 2015 27

Summary and Conclusions

The temperature of the porous medium in the immediate vicinity of the steam

injection well is significantly less (approximately 150 0C) than that of the steam

inside the well bore (approximately 230 0C).

The change in temperature in the porous medium around a steam injection well

is affected by:

The insulating properties of the well bore casing and grout system

Formation hydraulic conductivity and thereby groundwater velocity

(efficiency of the groundwater to “flush” heat away from the well bore)

April 30, 2015 28